1. Field of the Invention
The invention relates to a haloalkaliphilic hydrogen producing microorganism Halanaerobium sp. strain sapolanicus and methods of biohydrogen production using the same.
2. Description of Related Art
As the price of fossil fuels increases with diminishing reserves, biofuel production is seen as a viable contribution to current as well as future energy demands. Biohydrogen (H2) and ethanol generation from microbial fermentation of plant materials holds promise, with H2 having the advantage of producing only water vapor from combustion with oxygen.
Fibrous plant material is made up of lignocellulose and principally contains cellulose, hemicellulose and lignin. Cellulose and hemicellulose are more easily hydrolyzed, while lignin is recalcitrant to bacterial degradation. Thus, pretreatment of the biomass is necessary prior to microbial fermentation to separate the lignin from the cellulose and hemicellulose. The most common pretreatment method is steam blasting or steam explosion. Steam blasting requires electricity to produce the high heat and pressure necessary for steam generation, a usually natural gas- or coal-dependent step. As a consequence, considerable amounts of CO2 are emitted by this process. Further, compounds that are inhibitory to the subsequent fermentation process are generated by lignin degradation, including weak acids, furan derivatives, and phenolic compounds, which must be removed in a separate detoxification step. Overall, the process of pretreatment steamblasting, detoxification, and subsequent fermentation is relatively inefficient and is still fossil fuel-dependent, thus counterproductive to the goal of reducing greenhouse gas emissions.
An effective alternative to steam blasting is alkali pretreatment of the lignocellulose. Acidic pretreatment methods are also known. Exposing the biomass to high pH separates cellulose and hemicellulose from the lignin, and reduces (breaks down) the crystalline cellulose structure thereby making it more accessible for degradation and fermentation while limiting production of inhibitory compounds or CO2. However, the resulting substrate slurries are highly alkaline and have a potentially high concentration of salts, thus requiring a separate neutralization step prior to fermentation methods.
Microbial fermentation processes include both photofermentation and dark fermentation. Dark fermentation is the fermentative conversion of organic substrate to biohydrogen without the presence of light. The efficiency of dark fermentative production of H2 depends on the pretreatment of the substrate and operating pH. In addition, most organisms are not suitable for extreme conditions such as high temperature, or extreme acidity or alkalinity. Thus, a neutral pH is preferred.
Although the potential exists for microbially generated fuels from biomass to be an economically viable energy substitute, several issues are still to be resolved. Existing processes still require energy input of steam blasting pretreatment of the raw biomass, detoxification of the resulting compounds that are inhibitory to fermentation, and overall have low hydrogen yields. In conventional biohydrogen production, 80-90% of the initial biomass remains in the form of volatile organic acids and solvents such as acetic, propionic, butyric acids, and ethanol. Thus, there is a need in the art for improved biohydrogen production methods that eliminate the need for steam blasting, detoxification, or pH neutralization.